Awesome. This was a recent fix, to generate the proper code. When the GridPanel is a child of another component, the GridPanel is configured as a pure JSON object. This previously made the CheckboxSelectionModel hard to dynamically add to the Grid's column model. In a near future release we will be generating an autoRef for the grid automatically if it doesn't have one explicitly set. As well as the ability to re-order the CheckboxSelectionModel amongst the rest of the columns. At this point, I think most people would choose to have it in the first column position anyways :-)